1. Field of the Invention
The present invention relates to a hydroxygallium phthalocyanine pigment, a process for the production thereof, a process for producing a photosensitive layer-forming coating solution, an electrophotographic photoreceptor, a process cartridge, an electrophotographic device, and an image formation method.
2. Description of the Related Art
As photoconductive materials to be used in electrophotographic photoreceptors there are normally known various inorganic and organic photoconductive materials. In particular, these organic photoconductive materials have heretofore been proposed, studied and developed in various ways because they are advantageous in that they can form an electrophotographic photoreceptor having a good film transparency, film-forming properties and flexibility and are harmless and available at relatively low cost. Further, there has been a growing demand for the expansion of the wavelength range at which the photoconductive materials are sensitive to the wavelength range of semiconductor laser for the purpose of application to digital recording devices such as laser printer, digital copying machine and facsimile as photoreceptor. Several organic photoconductive materials for semiconductor laser have been already proposed. Among these photoconductive materials, phthalocyanine compounds have been reported much on the relationship between their crystal form and electrophotographic properties.
It is known that phthalocyanine compounds normally show many crystal forms depending on their production process or treatment process and thus show a change of photoelectric properties with crystal form. Known examples of the crystal form of phthalocyanine compounds, in case where they are metal-free phthalocyanine crystals, include α type, β type, π type, γ type and X type crystal forms. Further, gallium phthalocyanine pigments, too, have been reported much on the relationship between their crystal forms and electrophotographic properties. It is reported that a hydroxygallium phthalocyanine pigment having an extremely high sensitivity and diffraction peaks at positions of 7.5°, 9.9°, 12.5°, 16.3°, 18.6°, 25.1° and 28.3° in a Bragg angle (2θ±0.2°) of the X-ray diffraction spectrum using CuKα characteristic X-ray and an electrophotographic photoreceptor comprising such a hydroxygallium phthalocyanine pigment are excellent in photosensitivity, repeatability and environmental stability (see Journal of Imaging Science and Technology, Vol. 40, No. 3, May/June, 249 (1996), Journal of Imaging Science and Technology, Vol. 40, No. 3, May/June, 249 (1996) and JP-A-7-53892).
However, the related art hydroxygallium phthalocyanine pigments are disadvantageous in that when used as a material of electrophotographic photoreceptor, they can not be dispersed sufficiently in the binder resin for electrophotographic photoreceptor or cause scattering of properties such as sensitivity, charge ability and dark decay rate, easily causing image quality defects such as fogging and black or white spots. Thus, the related art hydroxygallium phthalocyanine pigments are not necessarily satisfactory in electrophotographic properties. Further improvements in hydroxygallium phthalocyanine pigments have been desired.